1. Field of the Invention
The present invention relates to a method of processing semiconductor wafer substrates and, more particularly, to a method of vapor phase etching.
2. Description of the Related Art
Wet etching and dry etching have been used as methods of etching oxide films and the like on the surface of semiconductor wafers. A recent trend toward devices of higher level of integration has result in more attention to the latter method, i.e., dry etching. Conventional vapor phase etching processes use a HF gas or a mixed gas of HF and H2O as the etching gas and remove natural oxide films and the like through a chemical reaction.
However, by-products produced during etching can remain on the surface of wafers depending on the material to be etched, resulting in a problem in that other chemical reactions can be caused by such by-products. Therefore, a method is normally adopted wherein dry-etched semiconductor wafers are cleaned using pure water.
The cleaning is followed by a process of drying the semiconductor wafers. Methods of drying at this stage include a spin dry process wherein the semiconductor wafers are dried while it is rotated, an alcoholic gas process wherein an alcoholic gas at a temperature higher than that of the wafers is condensed on the surface of the semiconductor wafers and the alcoholic gas is supplied until the wafer temperature equals the gas temperature to replace the moisture on the wafer surface with the gas, and a combination of both of those processes. Referring to the alcohol used for the alcoholic gas process, the use of isopropyl alcohol is disclosed in Japanese patent laying-open publication No. H6-29276 and the use of fluoroalcohol is disclosed in Japanese patent laying-open publications No. H3-106024 and No. H6-346096. A combination of the above-described spin dry process and the drying of a vapor of isopropyl alcohol (IPA) is disclosed in Japanese patent laying-open publication No. H7-66168.
The conventional spin dry process has had a problem in that a rotating mechanism used in such a process produces dust which contaminates semiconductor wafers. Further, a water mark has occurred on the surface of semiconductor wafers because of the atmosphere drawn into the rotation of such a mechanism at a high speed. In addition, a long period of time has been required to dry water droplets remaining on the inner wall surface of the reaction chamber after the drying of the semiconductor wafers is completed, which has reduced productivity.
Meanwhile, the alcoholic gas process has had a problem in that organic substances can remain on the surface of dried semiconductor wafers to cause contamination. The use of fluoroalcohol which is nonflammable instead of IPA which is flammable is not feasible on an actual production line because the cost of fluoroalcohol is prohibitively high, i.e., 20 times or more higher than that of IPA. Furthermore, the conventional process requires a tank of a large capacity because it uses a great amount of alcoholic gas, which has resulted in a problem in that the apparatus occupies a very large space.
It is therefore an object of the present invention to provide a method of etching which has no possibility of contamination and produces no water mark.
It is another object of the present invention to provide a method of processing semiconductor wafers which is economical and incurs a lower cost.
It is still another object of the present invention to provide a method of processing semiconductor wafers which results in higher productivity.
It is still another object of the present invention to provide a semiconductor processing apparatus which occupies a smaller space.